1. Field of the Invention
The present invention relates to a novel composition for modeling material.
The modeling material herein referred is the material for shaping model or pattern of any desired shape by cutting by hand-work or machine-work.
The model or pattern includes the following examples without being limited to them.
(1) Pattern for forming a sand mold which is used for casting of metal such as iron or aluminum.
(2) Model for casting of gypsum or epoxy resin.
(3) Profiling model for the cutting or machining operation of metal, resin, wood, etc.
(4) Mock-up model.
(5) Test cutting material for the examination of numerical control machine tools. The machine tool of the numerical control system is operated by a program. In order to examine the accuracy of the program applied, it is necessry to effect a preliminary cutting.
2. Description of the Prior Art
The modeling materials heretofore used includes wood materials such as Japanese cypress, Japanese white pine, Japanese cedar, and mahogany; resins such as epoxy resins and urethane resins; gypsum; and metals such as aluminum, zinc alloys, and iron. However, they are not satisfactory in both aspects of performance and price. Thus development of a new material has been desired.
For example, before production of a sand casting model pattern requiring a modeling material meeting the most severe requirements, a model is first made of wood inexpensively such as Japanese cypress or Japanese white pine, which is easy to subject to the cutting or machining operation, and the shape of the wooden model is transferred to a sand mold. Using this sand mold, a casting of iron, aluminum, or the like is empirically produced. The pattern may be corrected on a trial-and-error basis while confirming whether or not caves or voids are formed in the test casting, and whether or not the test casting is satisfactory is strength or size precision. The material of the pattern is finally determined with consideration for the necessary quantity of castings to be produced. In general, where the number of castings to be produced is supposed to be several hundred or less, the wooden pattern is used as such. Where the number is supposed to be less than 5,000, a pattern made of an epoxy resin is mainly used. Where the number is supposed to be about 20 to 30 thousand, a pattern made of an aluminum alloy is used, while a steel pattern is used in the case of the number being further larger. Why the material of the pattern varies depending on the scale of production is that the size of the pattern changes due to abrasion thereof by the molding sand. Even if the number of castings to be produced is smaller, steel or an aluminum alloy is used for a pattern required to have a high dimensional accuracy and a model having such a complicated shape that it is impossible to produce the pattern from wood.
The following performance characteristics are required of the modeling material. (1) It is uniform, and has neither voids nor pinholes in the inside. (2) It has good machinability and freedom of shaping in manual and mechanical operations. (3) It has good dimensional stability and accuracy. (4) It has adequate rigidity, toughness, and surface hardness. (5) It is desired to have good adhesion. In the case of a pattern for a sand mold, the modeling material is required to further have, for example, the following performance characteristics. (6) It has good abrasion resistance against molding sand. (7) It has good chemical resistance against a curing agent, etc. contained in the molding sand. (8) It has good releasability from the molding sand. (9) It is easy to repair.
The most inexpensive modeling materials widely employed are natural wood materials such as Japanese cypress, Japanese white pine, or mahogany. However, large trees of 600 mm or more in diameter suitable as the modeling material have recently been less and less available owing to gradual exhaustion of wooden resources. Even if such trees can be acquired, sufficient drying thereof for one to two years is necessary before they can be used as the modeling material. If the drying is insufficient, the wood material is subject, after cutting machining operation, to marked dimensional changes and deformation, occasionally leading to breakage thereof. Large storing space and inventory burden during the drying period cannot be neglected.
The biggest defect of wood as the modeling material is marked dimensional changes due to moisture absorption or desorption, particularly a large anisotropy in dimensional changes (tangential direction:radial direction:axial direction=10:5:1.about.0.5). Even a high quality Japanese cypress having the best dimensional accuracy is 0.14 to 0.27% in average tangential shrinkage (dimensional change rate due to a 1% decrease in water content from a water content of 15%). Furthermore, only straight-grained wood materials can be employed as the modeling material, while cross-grained wood materials are subject to too large warping to employ as the modeling material. Wood materials of the portion close to the bark, such as sapwood, are excluded from use as the modeling material, too.
It is believed that the wood material is excellent in machinability as compared with other modeling materials. However, this applies only in the case of manual processing by means of a chisel or a plane used by a woodcraftsman. In the machining opration by a machine tool, the feeding direction of the tool may be either along the grain, namely along the growth direction of wood, or against the grain. When it is against the grain, the wood may be cleft, making the machining operation impossible. For this reason, many wooden models are protruded models, while recessed models as profiling models for stamping forging are seldom wooden. Further, in the ball end mill processing, fluffing of a wood fiber occurs, requiring sanding after cutting by a cutting tool. In the cutting or machining operation at slow revolution by a metal processing machine, a wood fiber can not be sharply cut and hence fluffing occurs. Thus an exclusive wood processing machine capable of rapid revolution is required. Production of a wooden model for a portion of a small thickness such as a radiator blade of an air-cooled engine or a portion of an acute angle of 90.degree. or less encounters a serious difficulty, since breakage of wood during the cutting or machining operation may occur due to a low tenacity of wood. Even if the cutting or machining operation is completed after many troubles, the wooden model may be subject to unexpected deformation due to moisture absorption caused by a weather change. As described above, a stable model of high dimensional accuracy is limited in production thereof from wood.
A large amount of epoxy resins and urethane resins are used for a pattern having higher dimensional stability and abrasion resistance than the wooden pattern. However, since cutting of a resin by a cutting tool is almost impossible, a resin model is produced by a casting method comprising first preparing a wooden model, transferring the shape of the same to a gypsum mold, and casting an epoxy resin thereinto to effect reverse transfer. Therefore, casted epoxy resin models are naturally expensive, and the delivery time thereof is liable to be long, as compared with wooden models. Furthermore, the resin model produced by casting may frequently have voids or pinholes inside, and is poor in releasability from sand in the case of use thereof as a casting pattern. It is apparent that aluminum alloys and copper are much poorer in machinability than wood.
The model industry is making efforts to achieve a high dimensional accuracy of models and to realize a short delivery time as well as a price cut. Thus development of a material satisfying various performance characteristics as hereinbefore mentioned under (1) to (9) has been earnestly desired.